An implementation supertype for both Gaussian and Box filter based shadows to facilitate their conditional usage inside the various composite shadow effects like DropShadow and InnerShadow. The radius, width and height parameters all refer to the corresponding dimension that a "Gaussian" blur filter would use - other shadow implementations will have to use whatever parameters produce a similar effect. The width and height parameters should relate to the radius parameter by the equation w,h = 2 * r + 1 and if the width and height are set to something different then the radius parameter will be an average of the corresponding individual dimensional radius values.